1) Field of Invention
This invention relates to a phase shift mask capable of transferring patterns with an improved resolution upon placing phase differentials between exposure light rays that pass through the mask, a phase shift mask blank as a material for the phase shift mask, and a manufacturing method for the phase shift mask, and, more particularly, to a half tone type phase shift mask, and blank and manufacturing method for the mask.
2) Related Arts
It has been recently turned out that mere increase of numerical aperture of exposure apparatus' lens or mere reduction of wavelength of exposure apparatus' beam cannot improve practical resolution for lithography, since two key factors, rendition of higher resolution and assurance of depth of focus, required for lithography are in a trade-off relation.
Under this situation, phase shift lithography is getting attentions as lithography of the next generation. The phase shift lithography is a method to improve photo lithography's resolution by changing only masks without changing any optical system, and can grossly improve the resolution in using interference between transmission light rays upon placing phase differentials between exposure light rays that pass through the photo masks. Such a phase shift mask is a mask in common possession of light intensity information and phase information, and is categorized in several types such as, so-called Levenson, auxiliary pattern, self-aligrment (edge enhancement), or the like. Those phase shift masks have more complicated structures in comparison with those of conventional photo masks which possess only light intensity information, and require a higher level of technology in regard of manufacturing.
As one of such phase shift masks, a phase shift mask referred as to a half tone type phase shift mask has been developed these days. In such a half tone phase shift mask, its light translucent portion (photo semi-transmission portion) produces a light shield function in which exposure light is substantially shielded and a phase shift function in which phase of light is shifted (ordinarily reversed), and therefore, the half tone phase shift mask, without necessity to form separately a light-shield film pattern and a phase shift film pattern, has a feature that the structure of the mask can be made simple and that a manufacturing process of the mask can become easy.
A typical conventional half tone type phase shift mask is shown in FIG. 1. The half tone type phase shift mask has on a transparent substrate 1 a mask pattern, which is as shown in FIG. 1(a) composed of a light transmitting portion (a photo transmission portion) (exposure areas of the transparent substrate) 2 through which light with intensity capable of substantially contributing to the exposure process passes, and a light translucent portion (light shield and phase shift portion) 3 through which light with intensity unable to substantially contribute to the exposure process passes. The phase of light passing through the light translucent portion is shifted, and the phase of the light that has passed through the light translucent portion thereby enters a substantially reverse relation with the phase of light that has passed through the light transmitting portion (see FIG. 1(b)); lights passing through boundaries or their vicinities between the light translucent portion and the light transmitting portion and diffracting as to encroach one another due to diffraction phenomenon behave to cancel one another; the light thereby improves the contrast at the boundaries, or the resolution, while the light intensity around the boundaries are nearly nullified.
Meanwhile, the light translucent portion for the half tone type phase shift mask described above must have the optimum values for the transmittancy or transmission rate and the phase shift amount. It has been known that such optimum values in a phase shift mask can be realized by a single layer of the light transmitting portion. Such a phase shift mask has a light transmitting portion made by a thin film made of, as a material or materials essentially, metals such as molybdenum, silicon, and oxygen. They are such as molybdenum silicides, more specifically, oxides of molybdenum silicon ("MoSiO system material"), or nitride oxides of molybdenum silicon ("MoSiON system material"). According to those materials, transmittancy can be controlled by selecting the containing amount of the oxygen or the nitrogen and oxygen, while the thickness of the thin film can control the phase shift amount. When formed of those materials, the light transmitting portion can be structured by a single layer film made of a single kind material, thereby simplifying the film formation process in comparison with a case where it is made of multilayer film made of multiple materials, and thereby simplifying the manufacturing process since a single etchant can be used.
However, the molybdenum silicide film or the molybdenum silicide nitride oxide film, as elements composing the light translucent portion of the phase shift mask is weak against acid, such as sulfuric acid, used for primer or rinse fluid for rinsing during mask manufacturing or when masks are used. In particular, where the transmission rate and phase shift amount of the light translucent portion is set for KrF excimer laser beam (248 nanometers), the attenuation constant (K) must be small, and to realize a small attenuation constant, degree of oxidation or nitriding oxidation has to be increased sufficiently. If the oxidation degree is so increased, acid resistance of the light translucent portion is significantly lowered, thereby raising a problem that the transmission rate and phase shift amount thus set may be deviated.
While a film for phase shift mask blanks is formed, oxide tends to deposit on target surfaces, especially on non-erosion areas as the degree of oxidation or nitriding oxidation increases, and makes electrical discharge of the film unstable. Consequently, the transmission rate and phase shift amount is poorly controlled, thereby raising a problem that the blanks are formed with defects. Moreover, since the relationship between the composition of the film and film characteristics such as acid resistance, photo resistance, conductivity, deflection rate (thickness), transmission rate, selectivity of etching, etc. remains unsolved, the optimum film characteristics cannot be obtained in consideration of the manufacturing process or the likes even if the required optimum values for both of the transmission rate and the phase shift amount are obtained at the stage of blanks, and therefore those values are deviated from the designed or set values through experiencing the manufacturing process, resulting in disability to form the optimum phase shift masks.